3. Printhead cable failure
The connecting cables for the print head in general-purpose pin printers generally use plastic flexible ribbon cables (flat cables). Printhead cable failure is generally checked by the resistor of the multimeter. The method is to put the two pens of the multimeter on the corresponding lines at both ends of the checked cable, measure whether the resistance value is zero, and if necessary, bending tests should be performed at the crease to observe whether the measured resistance value on the multimeter has changed. Once the cable is diagnosed with a broken wire, the same printhead cable must be replaced. The broken parts cannot be treated by welding. Otherwise, if you are not careful during use, it will cause a signal short circuit. In severe cases, it will cause a signal short circuit to the ground (rack), causing the main control circuit of the needle printer to fail.
When the printhead cable has a crease and is not broken, a piece of adhesive tape about 1.5 cm can be cut off, and then stick it to the middle of the tape with a length of about 0.5 cm and a width of the adhesive tape to prevent the middle of the tape from being stuck together with the cable. Then bending the cable slightly outward at the crease, allowing the paper to align the crease, and stick the tape to the cable wire. In this way, the tension generated by the tape sheet will always force the cable to bend slightly outward at the crease, thereby causing the cable to produce an appropriate outward tension at the crease. This can reliably avoid the right movement of the print head during printing, causing the cable to be folded at the crease, and prevent the signal line in the print head cable from breaking.
2. Maintenance of car failures
Under normal circumstances, the left and right displacement of the chariot in the needle printer chariot mechanism should be smooth and stable. In this way, after the printer is turned on, no matter where the chariot is in its original position, it can return to the original position at the left end. When the printer is working, the chariot carries the printhead and moves back and forth. If the font car fails, the printhead will not move in place or not move at all, resulting in the printing work being unable to be completed.
The order of inspection of the word car is generally: printer word car mechanism (mechanical fault)----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
There are mainly the following types of car failures:
1. Too much dirt in the zipper mechanism often causes the zipper to fail to return to the position smoothly. At this time, cleaning methods can be used to troubleshoot the fault.
2. The mechanical failure of the font car mechanism, such as the wear of the font car belt, the parallelism of the front and rear guide rails, etc., will also prevent the font car from returning to position and moving smoothly. In this case, you can only replace the font-car belt or font-car guide rail.
3. The fault of the car motor, and the fault of the byte motor itself is mainly caused by the burnout of one or more phase winding coils of the stepper motor (short circuit, open circuit). This fault can be directly measured by a multimeter to measure the DC resistance value of the motor coil winding and then compared with the normal resistance value (generally, the four sets of coils of the motor will not burn out all, and there are always one or more groups that are good) to make a judgment. If one or both phases of the motor coil are burned out, as long as the coil frame does not deform (the rotation shaft rotated by hand is not obviously stuck), you can burn it by yourself according to the original wire diameter and number of turns of the motor (when removing the burned coil, pay attention to count the turns and then use a centimeter to measure the wire diameter). If the coil frame of the motor has been severely deformed, a new motor should be replaced. In addition, during the long-term use of the printer, due to vibration and other reasons, the magnetic steel in the motor may demagnetize, resulting in insufficient rotation torque of the motor, which makes it difficult for the printer to move the car during the printing process. In this case, you should replace the new motor of the same model.
4. Switching circuit failure. For printers that use the "high voltage drive low voltage lock" motor drive system, such as ARＲ-3240, ARＲ-2463, AR-3200, LQ-1500, LQ-800/1000 printers, there are often breakdown or open circuit between the transistor c～e that supplies high voltage in the high/low voltage switching circuit. If the c~e poles break down, the driving high voltage will be applied to the winding of the stepper motor, which may further cause the motor winding to burn out and burn out the transistor used as the phase signal of the stepper motor. If the circuit is open between the c~e poles, the high voltage cannot supply the motor of the car, and the motor does not run, the car will not move. In addition, it is possible to fail in the control signal part of the high/low voltage switching. At this time, it should be detected and eliminated according to the circuit of the specific printer model.
5. After the printer is powered on, if one or two sets of open circuits are opened on the four-phase windings of the stepper motor, the word car will shake in its original position or the word car is weak, or even the word car does not move. This phenomenon may be due to poor contact or disconnection of the plug of the zipper motor, or the phase control part of the zipper motor control and driving circuit. Since the circuits of various printers are different, specific circuits should be analyzed and tested, fault points should be found, and eliminated.
6. The stepper motor driver or its peripheral components are damaged. Stepper motor drivers are some printers used to control transistors or special integrated circuits to drive motors. For example, the chariot stepper motors in the AR-3240 printer and the M-2724 printer use transistors D1579 and D1789 as their respective chariot motor drivers, while the SLA7026M is used as the chariot motor drivers in the DLQ-2000K, AR-4400 and CR-3240 printers. If these devices are damaged, the chariot will not work normally. Only by replacing damaged components can you troubleshoot the fault.
7. The special gate array circuit failure of the word car motor drive circuit is controlled by the CPU through the special gate array circuit (such as E05A09BA in the LQ-1600K printer) or the I/O interface circuit (such as E05A24GA in the DLQ-2000K printer and XBL-2 in the AR-3200 printer). If this part of the circuit is damaged, it will affect the normal operation of the car, and even the car will not return to its original position when the printer is powered on.
3. Inspection and repair of sensor failures
The printer sensing circuit is an important part of the printer's core control circuit. The printer sensor sends the detected signal into the printer's microprocessor, causing the microprocessor to issue corresponding processing instructions.
There are many types of printers, and the types of sensors are also different. According to their structure and working principle, the sensors in the printer can be divided into: mechanical position sensors (using the closing and pop-up of the spring blade as the printer state recognition detection signal), photoelectric coupled sensors (divided into a blocking photosensitive sensor and a reflective photosensitive sensor), printhead temperature detection sensors (using a thermistor with a negative temperature coefficient), piezoelectric sensors (using piezoelectric crystals to detect the amount of ink and are installed inside the ink cartridge), and thin-film pressure sensors (mainly used in inkjet printers, used to detect whether there is ink in the ink cartridge and are installed inside the ink cartridge).
1. Fault repair of initial position sensor of font car
(1) Fault analysis: The initial position sensor of the car consists of the HOME sensor and the corresponding circuit. HOME sensors include photosensitive blockers and reed switches:
1) The initial position detection circuit of the cart composed of a photosensitive shutter. When the initial position sensor of the font car consisting of a photosensitive blocker fails, there are three main fault phenomena:
① After the printer is powered on, the carriage does not return to its original position, but moves to the left until it hits the left wall. The reason is generally that too much dust accumulates on the photosensitive blocking device, which affects the light beam of the photosensitive transistor receiving the light emitting diode. Another situation is that the device of the photosensitive blocker is aging, resulting in a decrease in the reception sensitivity of the phototransistor.
② When the printer's font car returns to its initial position, it hits the left wall panel and calls an alarm. The reason is that there is a short circuit in the HOME sensor detection circuit, causing the detection input port of the CPU (or gate array circuit) to always be at a low level. The following method can be used for the inspection of such faults: first prepare a small blank (it is suitable to be able to block between the light emitting diode and the phototransmitter of the photointerrupter), then pull the cart to the right side of the printer, then turn on the printer power, and quickly insert the small blank between the light emitting diode and the phototransmitter of the shutter and pull out to observe whether the cart stops moving at this time. If the car can stop moving, it means that the photosensitive shutter is working properly; otherwise, it is a photosensitive shutter failure.
③ After the printer is powered on, the word truck stops moving after moving for a short distance, enters offline state and alarms. This phenomenon is generally caused by the detection input port of the CPU (or gate array circuit) being at a high level. There are two possibilities for this kind of fault: one is the open circuit between the photosensitive shutter and the circuit board (connection line is broken); the other is the open circuit of the photosensitive shutter's photosensitive shutter. In this case, it is the method of measuring the positive and reverse resistance of the photosensitive shutter's photosensitive shutter.
2) The initial position sensor of the car made of reed switch.
In LQ-300K, KX-1121 and other printers, reed switches are used as the initial position sensor of the car. When the chariot returns to its initial position, the chariot hits the reed switch, and the reed switch contacts close and quickly disconnect before the printing procedure can be performed. As the printer's usage time increases, the reeds of the reed switch will weaken due to fatigue, that is, the switch fails. If the reed switch fails, although the car can return to the initial position, it cannot print normally. This kind of fault can generally be directly checked with a multimeter.
2. Maintenance of paper sensor
Generally speaking, only one paper-out detection sensor is installed on the printer, while for printers with front and rear feed slots such as LQ-1600KⅢ, LQ-1600K4 and LQ-1900KⅡ, etc., they are equipped with more than two paper-out sensors to meet the printer's paper feed processing needs for different locations.
(1) Checking for paper-out sensor and its detection circuit failure
There are generally three types of paper-out sensors for printers:
1) Paper-out sensor composed of reed switch
A reed switch is a mechanical switch of normally closed (or normally open) contacts. Various printers use corresponding reed switches of normally open or normally closed contacts according to the different signal levels (high or low) of their detection circuits. As the printer's usage time increases, the reed switch will weaken its elasticity due to fatigue, that is, the switch fails. This causes misoperation of paper-to-paper detection, which is manifested as although there is paper on the printer, the paper-to-paper indicator light on its operating panel is on and the printer does not print. This kind of fault check method is relatively simple. Just unplug the output plug of the sensor from the main control circuit board, connect it to its output plug with a multimeter (placed on the RXl barrier), and then insert a piece of printing paper on the printer's paper-feeding path (at this time the paper-feeding lever is in the sprocket paper-feeding position) and pull it out. This is repeated several times, while observing whether the pointer on the multimeter responds. If there is a reaction, it means that the reed switch is normal and its detection circuit should be further checked; if there is no reaction, it means that the switch fails, and the switch should be removed and repaired or replaced.
2) Paper-out sensor composed of photosensitive blocker
The structure and working principle of the photosensitive shutter used to detect the printer's paper-out is the same as the HOME detection sensor for the initial position of the font car. However, there is a lever-type baffle between the light emitting diode and the phototransmitter of the paper-end photosensitive shutter: Like the initial position detection sensor of the word car, the reason for the failure of this paper-end detection sensor is that there is too much dust accumulation on the photosensitive shutter, which affects the sensitivity of the light beam of the phototransmitter to receive, thereby causing a paper-end detection error. When checking for failure of this type of detection circuit, you can first connect the multimeter (with DCl0V block) to the output socket of the photosensitive blocker, power up the printer, and then insert a piece of printing paper on the printer's paper-feeding path (at this time the paper-feeding lever is in the sprocket paper-feeding position) and pull it out. This will be repeated several times, and at the same time observe whether the voltage on the multimeter has changed (0~+4.5V). If the voltage changes within the above range, it means that the sensor is normal. At this time, further check its detection circuit; if the voltage does not change or the output voltage is very low (less than +3V), it means that the sensor is faulty, and the sensor should be removed to check its sensitivity. Most printers using this sensor are caused by lever-type blanks being stuck or falling off (due to improper use of printer paper jams), which causes the printer to always show paper outages.
3) Paper-out sensor equipped with reflective photosensitive sensor
Reflective photosensitive sensors are widely used in printer paper-to-paper detection sensors, such as: AR-3200Ⅱ, CR-3240Ⅱ, NEC-P3300J+, etc. The characteristics of this sensor are: when the printer has paper, the light beam emitted by the light emitting diode in the sensor is reflected onto the phototransistor via the printing paper, and the phototransistor is thus turned on and outputs a low-level signal PE to a certain input port of the CPU; when the printer is paperless, the phototransistor is turned off because it cannot receive the light beam emitted by the diode and outputs a high-level signal. After the CPU receives this high-level signal, it stops or terminates the current printing of the printer according to the requirements of the printer control program.
The reason for the failure of this paper-to-dip detection sensor is mostly because there is too much dust accumulation on the sensor, which affects the sensitivity of the light beam of the phototransistor to receive the light emitting diode. The phototransistor cannot be turned on. In this way, the sensor emits a high-level PE signal when the printer is powered on, which causes a paper-to-dip detection error. It is manifested as that although there is paper on the printer, the paper-to-dip indicator light on its operating panel is on and the printer does not print. The detection method is the same as the detection method of photosensitive shutter failure. There are also a few sensors that are damaged by themselves or the sensitivity of the phototransistor is reduced.
3. Inspection of printhead temperature sensor
When the printhead works for a long time continuously, overheating will inevitably occur. In order to avoid damage caused by overheating of the printhead, almost all needle printers launched by printer manufacturers have installed printhead temperature detection circuits; its temperature sensors generally use thermistor with a negative temperature coefficient, that is, thermistor with this resistance decreases as the temperature of the printhead increases in the printhead, and is used to monitor the current temperature of the printhead. When the temperature of the print head is higher than the upper limit temperature set by the printer, the printer stops printing, and the online light on the operation panel flashes. When the temperature drops, the printer automatically prints at half speed (half of the normal printing speed). It will not resume printing at normal speed until the temperature drops below the set lower limit temperature. The temperature monitoring range of the print head set by the printer varies slightly depending on the model of the machine.
When the printhead temperature detection circuit fails, false alarms often occur, that is, the temperature of the printhead is not high, but after the printer is turned on, it does not print after printing a few lines, and even alarms are made as soon as the printer is turned on. The reasons are generally caused by damage to the thermistor (resistance value becomes smaller, open circuit or short circuit), damage to components in the detection circuit (such as input ports of the detection circuit chip, capacitor leakage, etc.), open circuit of the printhead connection cable (mainly thermistor port), or disconnection of the circuit board.
When checking for faults in this part of the circuit, different inspection methods should be adopted according to the specific printer model. For some printers such as NEC P-3300J+, KX-1121, NEWMAXP-2000, which do not install printheads and can move normally during self-test printing, you can first remove the printhead from the printer and then turn on the self-test printing. If the cart can move normally, it means that there is a fault in the thermistor in the printhead and the printhead needs to be checked; if the fault still exists, the temperature detection circuit should be checked. For printers that must be installed with the printer's letter to move normally, such as AR-3200Ⅱ, LQ-300K, CR-3240Ⅱ, LQ-1600KⅢ, etc., the thermistor of the printhead should be checked first before checking its detection circuit.
4. Maintenance of stepper motors
The manufacturing accuracy of the printer stepper motor is high, and its faults are mainly manifested in the absence of paper feeding. To determine whether this type of motor is damaged, the following methods can be used.
(1) Measure its resistance based on the resistance value marked on the stepper motor. The stepper motor is divided into two windings. The structural form of the two windings is exactly the same. The resistance of the center end of each winding is symmetrical and equal to the other ends, and is consistent with the marked resistance value. The arrangement order of the leads of different motors is different.
When measuring, you can first use a multimeter to divide the leads into two groups (the one with each lead is connected to one group), and then use the method of measuring the resistance to find the center tap end of each group. The center end should face equal resistances on the other two ends and match the marked resistance value. If the resistance value is asymmetric or different from the marked resistance value, the motor may be damaged.
(2) Test with the power supply voltage marked on the stepper motor (or the operating voltage of the motor in the circuit). If there is no label on the motor, you can start by using a lower voltage and then gradually increase the voltage to test. One end of the power supply (both positive and negative poles can be) is connected to the center end of a certain winding, and the other end of the power supply alternately touches the other two ends of the winding (note that the touch time should not be too long). At this time, the stepper motor should rotate step by step, and each step should be equally strong, otherwise it means that the motor is damaged. During inspection, be careful not to test if there is a serious short circuit in the stepper motor winding, otherwise the power supply will be burned.
(3) Some stepper motors have two identical windings, but have no center tap ends. During measurement, you can first measure whether the resistance values of the two windings are equal, and should match the motor mark, and then use a power supply to test. During the test, the two poles of the power supply alternately touch both ends of each winding. At this time, the stepper motor should rotate step by step and be equally strong, otherwise the motor will be damaged. It should be pointed out that when the stepper motor is damaged, the stepper motor driving circuit should be checked at the same time.
5. Quick maintenance method of interface circuit
If the printer can print but cannot print the specified content, "@@@@@..." or other characters appear, and a similar failure occurs when self-test printing occurs, it is mostly due to damage to the interface circuit. The printer's interface circuit belongs to a digital circuit. If it is damaged, an integrated circuit detector can be used for detection. Since the models of the interface chip are roughly the same, the replacement method can also be used for maintenance. If it can work normally after replacement, it means that the interface chip is damaged. Most of the interface chips of new printers do not adopt direct soldering, but are installed using integrated circuit sockets, so it is not too difficult to replace them. For old printers, an integrated circuit socket can be soldered, which will facilitate maintenance.
6. Inkjet head cleaning system failure
Under normal circumstances, after the inkjet printer is turned on, the inkjet head is moved to the nozzle cleaning unit and executes the automatic cleaning nozzle program. The ink absorbing mechanism in the inkjet head cleaning system begins to absorb and clean the nozzle. After the cleaning is completed, the nozzle is sealed by the sealing rubber piece on the nozzle rack to ensure the cleaning of the inkjet head. When the inkjet head cleaning system fails, the nozzle error occurs during the cleaning process. At this time, the following processing can be performed:
1. Some parts in the inkjet head cleaning system are damaged, such as aging of sealing rubber parts. Damaged components should be replaced.
2. Main control circuit board failure. The main control circuit board must be replaced or repaired according to the inspection situation.
3. The paper-feeding motor is running abnormally. Since the driving of the cleaning unit in the inkjet head transmits power through a paper-feeding motor, the inkjet head cleaning system is naturally affected when the motor fails. Check and repair the paper-feeding motor. The motor should be replaced if necessary.
4. The motor drive part of the font car is faulty. Since the chariot returns to the initial position of the left end (some printers are at the right end), the paper-feeding motor can be turned from the drive paper-feeding mechanism to drive the inkjet head cleaning system and automatic paper feeder, etc., when the chariot motor drive fails, the chariot cannot move to the nozzle cleaning unit normally to perform the cleaning procedure. Check and repair the car motor and its driving circuit.
7. Maintenance of printhead cleaning and sealing device
The printhead cleaning and sealing device is an important device of the printhead, especially the cleaning and sealing device that separates the printhead is relatively complicated. The entire device is installed at the leftmost end of the print head movement slide rail, that is, the protective position or initial position of the print head. The device consists of three parts: a scraper, a wiper, and a shield with a suction device. The device mainly completes four actions: "scraping, rubbing, hooding, and sucking", so as to maintain the printhead and ensure its normal operation.
In this device, the "scraping and rubbing" device has a simple structure and is not prone to failure. At most, it is just a damage to the rubber product. It can be removed without using it, and has no significant impact on the printing effect.
"Cover" means a shield; its function is to seal the print head well when the printer is not in use, ensure that the inkjet port has a certain humidity and prevent the nozzle from drying out and blocking. The common fault is that it is not tightly sealed, and there are two main reasons for this fault: one is the deformation of the shield. The shield has a certain elasticity, and slight deformation will not cause lax sealing. If it is severely deformed or there are large impurities on the surface, it will cause lax sealing; secondly, the shield is not in place. During the operation, the shield has a range of motion in both radial and axial directions to facilitate coordination with the movement of the printhead. When the movement of the shield is restricted, it is impossible to accurately seal the printhead in the initial position. Both of the above faults can be directly observed, just adjust or replace the accessories.
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